According to statistics from the China Photovoltaic Industry Association, in 2022, the newly installed photovoltaic capacity in China was 87.41GW, a year-on-year increase of 59.3%; of which, distributed new installed capacity was 51.1GW, a year-on-year increase of 74.5%. With the rapid increase in installed capacity, the "distributed photovoltaic + energy storage" market is expected to expand rapidly in the next few years.
From a global perspective, among various safety accidents in photovoltaic power generation, electrical fires occur most frequently and cause the greatest losses. If it is installed on the roof of a factory or home solar power system, it can easily endanger personal safety. Through the analysis of many cases, it can be found that electrical fires are mainly caused by DC arcing.
Therefore, it is imperative to use DC arcing intelligent detection and fast shutdown technology (AFCI) in photovoltaic power generation systems to improve the safety prevention and control level of power stations. This article will introduce to you what an AFCI inverter is, its characteristics, its role in photovoltaic safety, and its current status of intelligent development.
Main content:
Challenges facing photovoltaic safety
Distributed photovoltaics, which have become popular on the side of power users, are mostly built in industrial or residential areas and have higher requirements for safety protection. However, due to the characteristics of distributed photovoltaics such as small unit capacity, dispersed sites, complex application scenarios and system forms, it is inevitable that there will be deficiencies in dealing with various electrical safety challenges.
From the perspective of electrical safety, AC prevention and control focuses on power supply quality and safety, while DC prevention and control focuses on accidents such as fire, electric shock, and lightning strikes. As far as the current situation is concerned, AC standards are relatively sound and security prevention technology is relatively mature; however, DC prevention technology still has a lot of to do for improvement.
DC arcing is the continuous spark generated by the current breakdown in the air at the breakpoint of the circuit. It is a difficult problem that needs to be solved urgently in DC safety technology. In general centralized photovoltaic systems, there are tens of meters of high-voltage DC wires of 600V - 1000V between the photovoltaic module array and the inverter.
Loose contacts, poor contact, broken wiring, aging and damage of insulation materials, etc. are all very easy to cause DC arcing, which will increase the temperature of the contact part to 3000℃ - 7000℃, thus causing fires and other safety accidents.
In the past, arc detection only supported lower-level certification requirements and was no longer able to meet the needs of continuous upgrading and iteration of distributed photovoltaics.
On the one hand, the input cable loop length in the traditional solution is only 80m, but in actual industrial and commercial scenarios, the distance between the inverter and the power station is much longer than this; on the other hand, the input current supported by the existing solution is only 14A , but the maximum current of the component has exceeded 20A.
Under this background, DC arcing intelligent detection and fast shutdown technology (AFCI: Arc-Fault Circuit-Interrupter) are highly expected and has increasingly become a new way to protect photovoltaic safety. In short, AFCI is a new function integrated into the inverter like 2000w pure sine wave inverter or 3000w inverter that can identify and cut off the arc as soon as it occurs to ensure the safety of the distributed photovoltaic system and avoid fire caused by high arc temperature.
Currently, UL and NEC safety regulations have mandatory requirements for arc detection functions for DC systems above 80V. Since a fire in a photovoltaic system cannot be extinguished directly with water, early warning and prevention are very important. Especially for color steel tile roofs, it is difficult for maintenance personnel to check fault points and hidden dangers, so it is necessary to install an AFCI inverter with arc detection function.
However, the threshold for AFCI inverter is relatively high. Some manufacturers provide integrated algorithm packages from suppliers and then debug them through different threshold parameters. In practice, they will encounter many obstacles that are difficult to overcome.
What is AFCI inverter
For photovoltaic systems with a DC side voltage exceeding 120V, it is recommended to install protection devices such as AFCI inverter and DC switches; if the DC cable from the photovoltaic module to the inverter exceeds 1.5 meters, it is recommended to add a quick shutdown device, or use optimizer, so that when a fire occurs, the high-voltage DC can be cut off in time to extinguish the fire.
AFCI, Arc-Fault Circuit-Interrupter, is an arc fault interrupter. It is a protection device that disconnects the power circuit before the arc fault develops into a fire or a short circuit occurs by identifying the arc fault characteristic signal in the circuit.
As a circuit protection device, AFCI's main function is to prevent fires caused by fault arcs and can effectively detect loose screws and poor contacts in the DC loop. At the same time, it has the ability to detect and distinguish between normal arcs and fault arcs generated by the inverter when starting, stopping or switching, and promptly cuts off the circuit after detecting fault arcs. The AFCI inverter is an inverter that supports this AFCI function.
Features of AFCI inverter
AFCI inverter has the following characteristics:
- AFCI inverter has effective DC arc identification capabilities and allows a maximum DC current of up to 60A;
- AFCI inverter has a friendly interface and can remotely control circuit breakers or connectors, etc.;
- Equipped with RS232 to 485 communication function, AFCI inverter can monitor the module status in real time;
- LED and buzzer can be used on AFCI inverter to quickly identify the working status of the module and provide sound and light alarms;
- The functions are modular and easy to be transplanted to various series of products.
Unlike off grid batteries system, the smart grid has new requirements for switching appliances, and the communication and networking of AFCI inverter will be realized. Intelligentization and related bus technology, communication and networking and other technologies will play a greater role. The serialization and standardization of AFCI inverter products will greatly enhance its application scope and role in terminal power distribution.
Intelligence of AFCI inverter
There are two main difficulties in the development of AFCI inverter: noise adaptability and scene adaptability.
- Noise adaptability:
The on-site operating environment of distributed photovoltaic equipment is complex. The arc detection algorithm and threshold setting in traditional solutions are mainly based on human experience and cannot be effectively distinguished when environmental noise is close to arc spectrum characteristics. In addition, when parallel connection and ground connection are encountered, In arc detection, because the background noise changes in different environments, it is difficult to accurately identify it at the current technical level.
- Scene adaptability:
As the current of photovoltaic modules and the power of a single inverter continue to increase, the length of the input-side cable and the maximum arc current in actual usage scenarios may exceed the test conditions given by the standard. The characteristic signal of the arc will gradually weaken as the current and cable length increase, placing higher requirements on the accuracy of detection instruments and algorithms.
So we can see that AFCI inverter needs to be proceeded from reality and improve adaptability to cope with the many pain points derived from the growth of distributed photovoltaics. Huawei has explored a new path to intelligentize AFCI inverter, which is of great significance to the development of photovoltaic safety.
The intelligent arc detection solution of AI BOOST AFCI Huawei supports input cable loop lengths up to 200m and input current up to 26A, and can effectively distinguish between noise and arcs to avoid false alarms.
At the same time, Huawei has joint solutions of inverter and optimizer, and they have strong anti-interference ability. It is the only manufacturer in the industry that is compatible with 0V fast shutdown and AFCI, which can realize component-level arc fault location positioning and ensure photovoltaic safety in all aspects.
Behind a series of breakthrough innovations, Huawei has been accumulating in the fields of ICT and artificial intelligence, as well as its pioneering integration of AFCI inverter and deep learning technology. Different from manual inductive design, AI can calculate and iterate massive data based on highly nonlinear models, find feature patterns in high-dimensional space, effectively distinguish feature signals with similar shapes, and constitute on existing pain points.
From technological innovation to the establishment of an industry standard system, there is usually a long way to go, and AFCI inverter is no exception, especially at a time when grid security and information security have risen to a higher strategic position, and its leap is directly related to the high-quality development of the optical storage industry.
AFCI Huawei solution has obtained TUV 63027 certification and the highest level certification L4 issued by CGC. Huawei is also a member of the IEC 63027 international standard preparation project team. Using AFCI inverter as a breakthrough point, Huawei is working hand in hand with the industry and related industry departments to promote the establishment of a new power system standard system of best solar inverter and eliminate safety risks from the root cause.
The construction and implementation of a new generation of safety standards are not far away. In Europe, Australia and other regions, many countries have adopted photovoltaic DC arc detection and rapid shutdown as necessary standards for rooftop photovoltaics.
In China, the National Standards Committee and the National Energy Administration jointly issued guidelines for the construction of a standard system, which will focus on formulating Relevant standards for the grid side, power supply side, load side, and energy storage side of new power systems. By 2030, China's new energy installed capacity represented by photovoltaics will account for more than 40%, and new energy power generation will account for more than 20%.
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